Our company is in the process of deploying this model. We are still developing the business rules but our market research shows if you can get the right VoIP package and combine it with 3CX, you'll have a powerful solution if the price is right.

I am actually after the solution, so would you have anything we can use / trial /beta?

I have been looking through 3CX and was about to deploy it, and have probably decided that I am going to go down the SaaS route as we do for our other business needs. We currently use Numberstore for number routing and Voipfone for actual sip extensions...